There is a pressing need to develop new classes of therapeutics for the treatment of psychiatric and neurological disorders. Despite this need, little progress has been made towards this goal over the last two decades. One explanation for this failure is that the cell-based screens designed to identify new lead compounds have traditionally utilized immortalized, non-neuronal cell lines. It becomes understandable, in retrospect, why past screens have failed to yield the hoped-for plethora of new and important classes of compounds given the extraordinary architecture and physiology of neurons compared to other cell types. A second possible reason for this failure is that most cell-based screens have utilized a target-based approach, in which a specific protein target is identified that may hold promise for the development of new therapeutics. However, the brain and how brain disorders influence its function remains a large mystery. This fact argues that the alternative of phenotypic-based screens may offer more promise. Phenotypic screens search for influences on particular cell biological phenotypes without knowledge of the specific molecular targets that influence the phenotype. We have developed a novel screening platform that employs primary cultured neurons and cell biological, phenotypic readouts to identify the influences of small molecules. The methodology is flexible, scalable, and offers numerous advantages over traditional approaches. In this project, we propose to develop assays using this platform for the processes of mitochondrial dynamics, including biogenesis, fission, fusion, protein import, branching, and damage. We will use fluorescent markers for mitochondria to follow mitochondria for such assays, and conduct three screens of small molecules for influences on mitochondrial dynamics once the assays are optimized. Mitochondria dysfunction is associated with multiple psychiatric disorders like mood disorders, schizophrenia and autism; and neurodegenerative disorders as well. Thus, this project promises a rich new resource that can be used to survey small molecules, RNAi, or gene overexpression effects on mitochondrial dynamics in neurons.